Project code: D-13-02
Team and Leader Dr D.C. Patterson and Steven Morrison
Organisations involved ARINI, Hillsborough
Background and Summary
It is often assumed that grazed grass is the cheapest forage available in Northern Ireland. However, recent costings suggest that grazed grass may not be as competitive as other forages, primarily as a result of poor pasture utilisation under grazing. The Northern Ireland dairy sector is a grass based production system but two key principles have been highlighted which need to be considered in developing grass-based systems.
If the grazing system adopted results in a major reduction in milk output per cow then the fixed costs per litre will increase. Alternatively, if the fixed costs of a farm are high and can?t be reduced easily then the grazing system adopted must be capable of sustaining relatively high individual cow performance. With the increased genetic potential of modern dairy cows and the high fixed costs on most NI farms, then it may be advised to opt for the second situation. The key issue for maintaining high genetic merit cows is to maximise their potential milk output. This indicates that changes in grassland management for high merit cows will be in the form of trying to improve intake characteristics and / or improve the nutritional quality of the grass itself.
Previous studies have shown that high herbage allowances of tall dense leafy grass in the sward maximise grass intake, however this system presents the problem of poor efficiency of utilisation of the grass herbage and may lead to deterioration of the sward. Under this management system dead material and stem fraction of the sward will increase unless the herbage remaining after grazing is reduced to a uniform short stubble height. This process is costly and wasteful and therefore a system that can utilise a greater proportion of the available herbage, whilst maintaining a high intake and animal performance, would reduce the management costs e.g. topping, and the actual cost of the herbage consumed.
This study will involve spring calving dairy cows under different grazing systems throughout the year and with different supplementation strategies in early spring and late autumn. The supplements on offer will be primarily whole crop wheat (WCW) and possibly maize silage and grass silage. The WCW is high is readily available carbohydrate but low in protein and should be a good complementary supplement for spring and autumn grass, which is high in protein but low in sugar. The different grazing systems will be either based on the traditional 18 ? 21 day rotation with high herbage allowances of tall dense grass or on shorter rotation lengths (10 - 15 days) with moderate height dense leafy grass grazed at a high herbage allowance.
The objectives of the study are to examine the effects of the grazing system and supplement types on:
a) Milk yield and composition
b) Animal health, fertility and body tissue reserves
c) Herbage chemical, physical and nutritional properties
d) Herbage intake and efficiency of grass utilisation
e) Dry matter intake and substitution rates
f) Animal grazing behaviour
The aim of the project is to develop new grazing systems that will increase the efficiency of utilisation of grazed grass and therefore reduce the cost of grazed grass consumed. The system will maintain high DM intake and high individual cow milk yield at grass. With the combination of these outcomes the overall result will be to increase financial returns to the farmer and promote the healthy green image of Northern Ireland dairy industry.